1. Field of the Invention
The present invention relates to a plastic optical lens and a molding method therefor, and more particularly, to a plastic optical lens having a surface with annular curves arranged in an area outside an optical effective diameter thereof and a molding method therefor.
2. Description of the Prior Art
With the development of portable devices, photographing lens assemblies are leaning toward a trend of being more compact. This requires the lens to have a smaller thickness and a shorter diameter. In the past, larger-size optical systems are provided with light-shielding sheets to filter out the flare/ghost. Such a shielding technique, however, is less applicable for a compact lens assembly. Therefore, a compact lens assembly may be provided with additional curved structures, e.g. a plurality of annular curves centering an optical axis, arranged in a region outside an optical effective diameter thereof to direct the unwanted light in the system to a place other than the image plane. In the conventional method, these curved structures are symmetrically disposed with respect to an optical axis. FIGS. 17A and 17B illustrate the flow of the molten plastics from the sprue gate (not shown) into the lens mold during the plastic lens molding process in which the conventional plastic injection-molding method is applied. As can be clearly seen from FIGS. 17A and 17B, the arrangement of these curved structures is one of the factors that hinder the flow of the molten plastics. As lenses now are made thinner, the resistance that hinders the flow of the molten plastics increases significantly. If the speed of the molten plastics flowing in a direction from the sprue gate toward a region of the lens mold corresponding to the center of the lens is not improved, molding defects, e.g. a void or a welding line shown in FIG. 17B, can be formed easily within the optical effective diameter region of the lens during the lens molding process. These defects not only reduce the production yield for the lens but also affect the optical performance of the lens.